The life expectancy of an asset engaged in the efficient running of a business. A milk float has a life expectancy of 20-30 years - it's hard to see something bigger and better replacing it. A PC may have a useful life of 2-3 years, as it's likely that a more efficient or cheaper version will render it obsolete. Important in leasing - for On / Off Balance sheets decisions.
Compare the lifespan of a building to a plastic carrier bag. Buildings stand and are used for centuries, carrier bags rarely get used more than once. Significant investment spend on a building would be appraised/counted over many years and deliver great benefits - over its whole useful life. Investment in a carrier bag wouldn't be assessed for more than one day.